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no power to fuel pump

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Jthorntom

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Not sure if i'm in the right forum.. I have a 1994 Glastron with 4.3, put new power steering pump on it, had it running noticed it wasn't charging looked at the wiring looked ok , let it run about ten minutes heard a pop motor died fuel pump quit working. now no power going to pump. what the heck happened?
 
Jthorntom said:
Not sure if i'm in the right forum.. I have a 1994 Glastron with 4.3, put new power steering pump on it, had it running noticed it wasn't charging looked at the wiring looked ok , let it run about ten minutes heard a pop motor died fuel pump quit working. now no power going to pump. what the heck happened?
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I think the fuel pump gets powered via the starter lug during cranking then goes through an oil pressure switch when in run position. This is a safety to keep the fuel pump from running if ignition is on but engine conks out.

If it wasn't charging would suspect alternator is defective or wired up wrong. Did it pop the 90 amp fuse on the positive starter lug. This is to protect from over charging. if it blows the fuse the it interrupts the battery positive supply. It is a small cube on the starter absolute MF to get to let alone put a volt meter on it. You can test and see if you have 12 v on the 50 a breaker on engine which also gets it power from the fuse...
 
I traced fuel pump wire it goes to a sensor on the side of the block, doesn't look like any oil pressure sensor I have ever seen, has 3 termanals 1 is empty, 1 to FP other 1 has 2 wires going somewhere. right now it's raining I have no cover to work under. That 50 amp breaker should be hot. I'll check that. just weird should run on battery on a fully charged battery.I figured ALT. bad. why pop a fuse? after it was running.
 
sounds like somebody put a different oil pressure switch on the block...being as it was running before, if it failed, probably easiest to replace it with the same...assuming you can identify it.

you can used a fused jumper, direct to the fuel pump, for troubleshooting purposes...
 
Did more checking , have power to 50 amp breaker power to alt. big wire. and the starter. That sensor screwed into oil port by the oil filter, is that safety switch. it has a wire coming from starter solenoid, then one goes to fuel pump. solenoid mounted on starter. that wire has no power with key on. bad solenoid??
 
no...should be connected to the R terminal on the starter's solenoid (little stud). The R terminal only has +12VDC when the solenoid is engaged (the starter is spinning).
 
the solenoid has 2 small studs, can't see witch one is R. one has the signal from the key it spins over the starter, other little stud goes to fuel pump.
 
Kinda said that wrong. wire coming from small stud of solenoid on starter, opposite of one that cranks engine, goes to that oil safety switch, 2 wires come from that sensor 1 goes to fuel pump 1 goes to ignition coil. shouldn't the wire coming off starter solenoid be hot with key on?
 
maybe this will help...

#8 is the oil pressure switch, #7 is the fuel pump.

The fuel pump is energized in two independent ways: 1) during engine cranking, the fuel pump received current from the R terminal on the starter's solenoid (the PUR/YEL wire in the diagram) and 2) from the PUR wire (fed from the IGN terminal of the key switch in RUN) AFTER the engine builds oil pressure (which turns that switch ON).

nothing at the fuel pump is 'hot' with the ignition key to RUN.
 

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  • 93-97 V-6 starter wiring.pdf
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I just don't understand, i see the diagram understand that but before this started when I go to start the boat the fuel pump runs with key on, then crank it and it would start.. now i got no voltage on the solenoid wire going to oil pressure switch. key on, cranking. don't matter my wire colors are different but looks the same set up. could that oil pressure switch have lost ground ? maybe why I'm not getting voltage there. I jumped 12 volts to the stud at starter nothing happens.
 
If that stud on starter only gets hot on crank, what keeps the power to the pump going after it starts? oil pressure switch has 3 terminals one empty one to fuel pump one to solenoid..I'm missing something. I really thank you for helping.
 
Yeah, I don't have that purple wire coming from ALT. going to repair the wiring at ALT. has butt connectors back to back on the wires wire 6 inches long both of them have 3 butt connections, looks like a 3 year old did it. thanks probly get new Alternator also. thanks for the help.
 
whatever you redo, DON"T ELIMINATE the oil pressure switch...you need a means to disable the fuel pump when the engine is not running...

having the fuel pump run when the key is in RUN is a safety issue...you want to fix things correctly....
 
Thanks again, Get this I ran 12 volts to the empty terminal on oil pressure swicth, tried to start started right up ran 2 minutes now no spark.......fuel pump works perfect. my test light bulb burnt out trying to rig one up. crazy ****.
 
I just had issues with the same oil pressure switch.

How this works is it’s a 3 terminal on/off/on switch with two power leads coming in, and the other going to the fuel pump. One is hooked to the starter solenoid and is only provides power to the fuel pump when the starter is engaged.the other power line is switched on when the switch detects oil pressure and stays on as long as the engine is running. If the engine dies for any reason the fuel pump shuts off…. That is the way it’s designed to work for safety reasons. If you have power to your fuel pump when you turn on the key , your wiring is wrong, and it’s dangerous…. Kirk
 
makomark said:
whatever you redo, DON"T ELIMINATE the oil pressure switch...you need a means to disable the fuel pump when the engine is not running...

having the fuel pump run when the key is in RUN is a safety issue...you want to fix things correctly....
Click to expand...

makomark said:
whatever you redo, DON"T ELIMINATE the oil pressure switch...you need a means to disable the fuel pump when the engine is not running...

having the fuel pump run when the key is in RUN is a safety issue...you want to fix things correctly....
Click to expand...
thought i would share this. What a mess.

bad news 001.JPG
 
kirkll said:
I just had issues with the same oil pressure switch.

How this works is it’s a 3 terminal on/off/on switch with two power leads coming in, and the other going to the fuel pump. One is hooked to the starter solenoid and is only provides power to the fuel pump when the starter is engaged.the other power line is switched on when the switch detects oil pressure and stays on as long as the engine is running. If the engine dies for any reason the fuel pump shuts off…. That is the way it’s designed to work for safety reasons. If you have power to your fuel pump when you turn on the key , your wiring is wrong, and it’s dangerous…. Kirk
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Thanks Kirk, i'm getting new alt' and redo the wiring where it works like it should. yeah it's missing the power feed wire from alt. they had it jumped off the ignition coil. has a 55 amp alt. wouldn't hurt to put a 65 amp on there? 47 bucks cheaper...
 
Jthorntom said:
Thanks Kirk, i'm getting new alt' and redo the wiring where it works like it should. yeah it's missing the power feed wire from alt. they had it jumped off the ignition coil. has a 55 amp alt. wouldn't hurt to put a 65 amp on there? 47 bucks cheaper...
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There is a difference between an oil pressure sending unit or sensor, and and an oil pressure switch. When you get your switch and get ready to hook it up, be sure and hook it to the right side of the starter solenoid. One side is hot when you turn on the key,nand the other lights up when the starter motor is engaged. That’s the post you hook to the oil pressure switch. The other hot wire goes to the automatic choke on mine, and quite honestly I haven’t a clue how an automatic choke works…lol
 
I would suggest if you dont know how your choke works, you shouldnt comment on how to wire a oil pressure switch.

It best to supply a schematic so its CLEAR what wires go where....which also means its best to get a Manual!!
 
I was kidding ghost…. A lot of this stuff is basic common sense. I was just trying to be helpful explaining how that oil pressure switch works. The same 12 volt power line feeding the electric choke also powers the oil pressure switch on mine….

As far as the manual goes…All these older 4.3 mercruiser motors that were carburetor models have mechanical fuel pumps. There is nothing in that manual regarding electric fuel pumps for carburetor models that I know of… I’ve looked.

Kirk
 
Mercruiser Service Manual #7 describes the older mechanical fuel pump v-6 engines...MCM Service manual #18 covers the GenIIs with the 'newer' options, including the fuel injection...
 
makomark said:
Mercruiser Service Manual #7 describes the older mechanical fuel pump v-6 engines...MCM Service manual #18 covers the GenIIs with the 'newer' options, including the fuel injection...
Click to expand...
So does this MCM service manual #18 show an electric fuel pump on a carborated model engine? Or just the fuel injected models?
 
Here is the deal,

At some point in the late '90's engine blocks stopped being machined for mechanical pumps. (All auto's went EFI)

So, based on the use of an electric fuel pump on the V6 that had been in use for years, they adapted it to the Carbed V8's.

Electric fuel pumps used for carbed engines produce ~ 6-8 psi.

Electric fuel pumps used for TBI and EFI produce much higher psi and CANNOT be used with carbed engines even if they look the same.

All fuel systems with electric fuel pumps have safety designed into them.

The carbed engines use a oil pressure switch.

I am not sure if #18 shows a carbed schematic or not as I am responding from my phone not my lap top.

I will try to look and let u know
 
Yes Manual 18 is for V6 with electric fuel pump.

Engines GM V6 Gen II Balance Shaft All 1993–1997 Service_Manual__18

Item 8 is the oil pressure switch

v6 electic fuel pump.jpg
 
I’m a bit confused with this diagram. The oil pressure switch on this dwg only shows two posts instead of 3 , and the line going to the starter solenoid has a T hooking to the switch and the fuel pump on one side, and the other coming from the alternator. While I can see this working just fine it is different than mine.

The way mine is set up is similar, and sounds like the OP has the same set up. On mine The alternator line goes to the automatic choke as does the line to the oil pressure switch feeding both the choke and fuel pump 12 volts when the engine is running. But mine has a second post on the oil pressure switch that runs directly to the starter solenoid, and the 3 rd post goes to the pump.

I’m really trying to be helpful and not just high jacking the thread. Often times these wiring diagrams are confusing, and once you add in some creative wiring some barn yard mechanic has done to your boat just to get things running doesn’t help matters.

In my case the only reason I’m well versed on how these switches work is I was doing a complete upgrade to my duel battery
System wiring and inadvertently disconnected a couple of the oil pressure switch wires when pulling my new battery cables around the back of the motor. It’s amazing the thing even ran at all with those tab connectors so loose and corroded. So I replaced the connectors and had to figure out how the switch worked. When the OP mentioned he had a 3 post switch with one empty… I thought maybe sharing my experience might be helpful. I’m not a boat mechanic per say, but do a lot of my own work when I can.

Speaking of which…. Can one of you experienced mechanics answer the OPs question on the alternator output? He’s suggesting going from a 55 amp up to a 65 amp. I cannot answer that question.

Can you guys see anything wrong with feeding the oil pressure switch from the same power line that feeds the auto choke like mine is set up? That would save the OP hooking another direct line to the alternator. Thanks for your patience guys. It’s a great thing to have experienced mechanics willing to share their knowledge on this forum. Kirk
 
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